1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, etc.
2. Discussion of the Background
Recently, in an image forming apparatus, a so-called front loading method having a front paper-feeding tray capable of advancing and retreating towards a front side of the image forming apparatus is becoming common. "Plain paper" that can be fed from the front paper-feeding tray has a thickness of 90 kg in Renryo (a unit of thickness of a paper represented by weight of 1000 stacked papers in each area of 788 mm.times.1091 mm provided by Japanese Industrial Standard) or less. In addition, special type papers such as a carton paper (hereinafter referred to as a "carton") that exceeds the aforementioned thickness, an envelope, a post card, an exfoliation paper, OHP paper (transparency film for an overhead projector), and other papers that are relatively thick can be fed by a by-pass paper-feeding device attached outside of a main body of the image forming apparatus, which is referred to as a manual paper feeder.
Generally, the front paper-feeding tray can contain about 250 to 1000 sheets of plain paper, and a separation paper-feeding mechanism such as a corner-pick separation device capable of separating paper even when a number of contained papers is large, which is provided at a relatively low cost, a friction pad, or the like, can also be used.
On the other hand, it is assumed that the manual paper feeder is generally used for special type papers, such as a carton having a low frequency of use, a special paper such as a paper for an overhead projection, a non-standard size paper, or the like, for a provisional use. There are two types of manual paper feeders, one that can hold only one paper at a time, and another one that can hold a plurality of papers at a time. The former is quite complex to use in requiring setting papers one by one, even though it is provided at a relatively low cost. The latter requires an expensive separation paper-feeding mechanism since several cartons or special papers may be fed one after another. In addition, the latter is not always advantageous in operation since, in a case of a carton as an example, only approximately one third of the number of plain papers can be set at one time. However, the number of users of the manual paper feeder having a high frequency of use cannot be disregarded, and the number of one time uses is large. Therefore, the manual paper feeder does not have sufficient specification even though the manual paper feeder can feed plenty of papers. On the contrary, many of the users of the image forming apparatus having the manual paper feeder capable of feeding plenty of papers sparingly use the manual paper feeder, which has an expensive mechanism.
Accordingly, in light of solving the problems of the aforementioned manual paper feeder, the present inventor thought that if a FRR (Feed Reverse Roller) or similar sophisticated separation paper-feeding mechanism is mounted on a front paper-feeding tray, functions of a manual paper feeder can be executed by the front paper-feeding tray. Consequently, availability for a sort-of-paper from the front paper-feeding tray expands to a great extent, and the manual paper-feeding function is not required. Further, when the front paper-feeding tray is used for plain paper, higher reliability of paper-feeding quality can be obtained.
On the other hand, many background image forming apparatus are provided with a peripheral device for paper-discharging (hereinafter referred to as a paper-discharging peripheral device). The paper-discharging peripheral device may be a sorter, a mail box, a finisher, a reversing unit for a duplex copy, or the like. In other words, the paper-discharging peripheral device discharges a paper on which an image is formed by an image forming apparatus. Since there scarcely is a request for using a carton or special paper in such a peripheral device, paper-feeding performance for paper other than plain paper is not assured because the paper-discharging peripheral device is manufactured at low cost. Further, the manual paper feeder is surely used when the carton or special paper other than the plain paper is to be fed, and accordingly a controller of the image forming apparatus controls not to convey the carton or special paper to the paper-discharging peripheral device from the manual paper feeder. Such a control is easy because the controller can easily recognize the existence or absence of paper from the manual paper feeder.
However, in a case of a construction that feeds the aforementioned carton or special paper as well as the plain paper with the front paper-feeding tray, the plain paper should be discharged to the paper-discharging peripheral device, whereas the carton or special paper should not be discharged to the paper-discharging peripheral device because paper jamming may tend to occur at the paper-discharging peripheral device. In addition, there is a problem that the user may not understand the cause of the paper jamming.
Further, in a case of manual paper-feeding, a setting temperature of a heat fixing device may be changed from that for the plain paper or an image forming condition may be changed from that for the plain paper, to improve a fixing property for the special paper, e.g. carton, or to maintain image quality. However, a kind of paper fed from the front paper-feeding tray cannot be distinguished when a background paper-feeding device is used. Accordingly, the setting temperature of the heat fixing unit and the image forming condition cannot be changed according to the type of paper, and a problem of insufficient fixing or poor image quality may occur.